The invention relates to the field of gas turbine engines, and more specifically, to gas turbines that maintain control of fluid density to control system operation and minimize losses.
A conventional gas turbine engine comprising a compressor, a turbine mounted downstream of the compressor, a heat exchanger, a heated fluid source connected to a source of fuel, and a source of combustion air, has a device for removing excessive waste fluid from the gas turbine engine flow duct and replacing it with air to sustain combustion and to control fluid density in the gas turbine engine flow duct to control engine power. The device for removing excessive waste fluid from the gas turbine engine flow duct is normally a throttling valve or an auxiliary turbine. To control the fluid density in the engine flow duct, the operator increases the fuel and the air supplied to the heated fluid source, and excessive waste fluid is exhausted from the engine flow duct by throttling or expanding in an auxiliary turbine. Throttling the excessive waste fluid into the atmosphere causes enormous energy losses. If the excessive waste fluid is expanded in an auxiliary turbine that is used for certain gas turbine engine or subsystems needs, a part of the energy from the excessive waste fluid is recovered. However, in both cases, the part of the waste fluid that is going to be exhausted first passes through the flow duct of the gas turbine engine and acquires a certain amount of energy which is irrecoverably lost after this part of the waste fluid has been exhausted. In addition, controlling the gas turbine engine by adding air into the flow duct to replace a part of the waste fluid and by removing the excessive waste fluid from the gas turbine engine flow duct by throttling or by expanding in the auxiliary turbine is rather sluggish because of the substantial inertia of the waste fluid mass in the flow duct. Accordingly, engine response is rather slow with this control method. Still another disadvantage of the prior art is the need to exhaust the hot waste fluid (at about 400xc2x0 C.) through a throttle valve or through an auxiliary turbine which because of the high temperature to which it is exposed must be constructed with more exacting manufacturing tolerances using special materials. The cost of such devices is rather high, and their reliability in operation is limited. Moreover, releasing hot gases into the atmosphere is environmentally unfriendly.
It is an object of the invention to provide a gas turbine engine which has a greater efficiency.
Another object of the invention is to provide a gas turbine engine which can be effectively controlled without sluggishness.
Yet another object of the invention is to provide a gas turbine engine which is easier and less expensive to manufacture and is more reliable to operate.
Finally, it is an object of the invention to lower the environmental impact of the gas turbine engine.
The above and other objects of the invention are accomplished by providing a gas turbine engine in which a compressor flow duct has a plurality of flow duct areas, each providing a different compression ratio, and a plurality of outlet taps, each communicating with a respective area of the plurality of flow duct areas. The engine has a turbine mounted downstream of the compressors and a heat exchanger. The inlet of the compressor is connected to a first outlet of the heat exchanger which has its first inlet connected to the outlet of the turbine. A second inlet of the heat exchanger is connected to the outlet of the compressor. A heated fluid source, which is connected to a fuel source, is provided upstream of the turbine and connects to a second outlet of the heat exchanger. The engine has a device for supplying combustion air to the gas turbine engine flow duct and also has an outlet tap switch which has a plurality of positions for selectively opening to the atmosphere one outlet tap and disconnecting the rest of the outlet taps from the atmosphere in each position of the switch. A switch control moves the switch to one position of the plurality of positions.
Other objects and advantages of the invention will become apparent from the following description of preferred embodiments thereof with reference to the accompanying drawings.